13 November 2008

A historic first for the recently down on its luck Hubble Space Telescope. The HST has taken the very first visible light pictures of a planet orbiting a distant star.

Taken with the Advanced Camera for Surveys, the image is of the planet this is known as Fomalhaut b. Formalhaut b orbits 10.7 billion miles from its primary Formalhaut, about two-thirds again farther from its sun than Pluto. It's calculated to have an orbital period of 872 years. Formalhaut b has upper limit of three (3) Jupiter masses set for it, because were it any larger, it would destroy the dust ring surrounding the star.

The white dot is the star Formalhaut. NASA and ESA scientists blocked the bright glare of Formalhaut so they could capture the planet Fomalhaut b, which is 1 billion times fainter than its star. The red dot at lower left is a background star.

The Fomalhaut system is 25 light-years away in the constellation Piscis Australis. It is white 1st magnitude star, with a mass of about 2.3 times that of our Sun and believed to be a young star. The Dusty disc is thought to be a proto-planetary disc and is offset from the center of the system by about 15 AU.

The existence of the planet was postulated because something was gravitationally modifying the bright inner edge of the dust ring that we can see here.

The planet does raise some interesting questions. It was much brighter than expected, leading some to speculate the existence of Saturn-like rings. The Formalhaut system is thought to be young, only about 200 million years old, versus 4.5 billion years for our Sun and it is expected to last only 1 billion years. Since the planet is so young, it should very hot due to gravitational contraction and very bright in the infra-red spectrum. As of today however, it cannot be picked up by any infra-red instrument pointed at it.

Those of you that live in the southern hemisphere or have access to Google Sky can see Formalhaut for yourselves, weather permitting.